The present invention relates to apparatus and method for transmitting data and, more particularly, to apparatus and method for transmitting variable-bit rate data on a digital serial bus having a predetermined transmission rate. The invention also relates to apparatus and method for transmitting variable-bit rate data on a digital serial bus with means for pre-determining the peak bit rate of the variable-bit rate to be transmitted.
As is known, various types of digital video-audio equipment, for example, DVD reproducing devices, digital VTRs, digital televisions, etc., are currently available for consumer use. Several such devices reproduce or receive digital video/audio signals, convert those signals into analog signals, and supply the analog signals to analog-type video/audio equipment. It is also generally desirable to supply from such equipment digital video/audio signals to, for example, a personal computer, a digital television receiver, or other type of digital device.
The communication system IEEE-1394 is a digital serial bus which has been proposed as a means for transmitting such digital video/audio signals between digital devices. Referring to FIG. 1 of the drawings, an exemplary block diagram of an IEEE-1394 system that includes an IEEE-1394 bus 901 and various digital devices 902-907 is shown. In the exemplary block diagram, the IEEE-1394 bus is coupled between a DVD reproducing apparatus 902, a digital VCR 903, a digital broadcasting receiver 904, a digital television receiver 905, a digital television receiver 906 and a personal computer 907. As shown, digital video/audio data is supplied from DVD reproducing apparatus 902 via the IEEE-1394 bus to digital television receiver 906, and digital video/audio data supplied from digital broadcasting 904 is supplied via bus 901 to digital television receiver 905. Given an IEEE-1394 bus with a transmission rate of, for example, 100 Mbps, and video/audio data is organized into "units" of data, then in accordance with IEEE-1394 standard, 4915 units of data can be transmitted during each 125 .mu.sec transmission cycle of the bus. In accordance with this standard, the number of units transmitted corresponds to the bit rate of the signal to be transmitted. For example, to realize a communication speed of approximately 10 Mbps, which corresponds to the mean bit rate of a typical video signal, then approximately 1200 units are needed. However, to realize a communication speed of approximately 2 Mbps, which is the mean bit rate of an audio signal, then approximately 704 units are needed.
One limitation of the above discussed IEEE-1394 standard is that signals are transmitted only after their transmission rate (i.e., bit rate) is determined. However, DVD reproducing devices that employ MPEG encoders/decoders reproduce digital video/audio data at a variable rate and, thus, an IEEE 1394-bus previously has been unable to transmit variable rate data reproduced from such devices.